1. Field of the Invention
The present invention relates to disk recorders in general and more particularly to an improved read/write head-positioning apparatus wherein the head-carrying portion is suspended upon fluid bearings and driven by a coaxial motor.
2. Description of the Prior Art
In order to store electrical signals representing, for example, computer data or television type video information, disk type video recorders are often employed. As the name implies, disk recorders employ one or more platter-shaped disks. The surface of each disk is of suitable material such that a read/write head which is maintained in proximity therewith may be used to selectively magnetize portions of the disk surface as the disk is rotated. To effectively utilize the entire surface of the disk, the disk is most commonly divided into a number of imaginary concentric rings or tracks, or it is divided into one long spiral track, either of which may be accessed by the read/write head when it is suitably positioned along a path which corresponds to a radial line of the disk.
It is no doubt apparent that the performance characteristics of a disk type recorder are determined in large part by how rapidly and accurately the read/write head may be positioned. To this end a number of read/write head-positioning apparati have been developed. One such apparatus employs a motor driven screw for selectively positioning a read/write head-carrying carriage. Although effective in head position, the apparatus is relatively slow.
Another prior art read/write head-positioning apparatus employs a carriage which engages a pair of guide rails through a number of bearings. A motor which is comprised of an electrically actuated coil that interacts with a magnetic field, develops a force which is used to drive the carriage along the rails.
Because the motor, and thus the positioning force developed by the motor, is offset with respect to the drag force developed between the carriage and the rail, a rotational moment is developed. As a consequence, this prior art head-positioning apparatus suffers from the major disadvantage that as the carriage is driven by the motor, an up/down rocking, or pitching, action of the carriage occurs which causes the read/write head to bounce up and down on the disk.
Additionally, an unbalanced perpendicular force is developed by the air pressure which is commonly employed to float the read/write heads. The force develops a moment which causes a yawing action of the carriage and thus the heads. By preloading the bearings, these problems are reduced as well as permitting the use of lower tolerance parts. Unfortunately, the preloading force develops a frictional force which reduces the accuracy of the head-positioning apparatus. In addition, this frictional force degradates the response time of the apparatus which is already relatively slow due to its relatively large mass.
Finally, this last mentioned prior art, head-positioning apparatus employs a relatively large number of high tolerance parts which require careful assembly and alignment. In other words, not only must the rails be aligned in direction and height with respect to the disk, but the rails must be aligned to the carriage, the motor aligned to the rails and the coil aligned to the motor.